1. Field of the Invention
The present invention relates to an operation system including an operating object device that operates when an operation member moves according to the force applied by a user, and an assist force applying device for applying assist force to the movement of the operation member such as an electrically operated power steering system.
2. Description of the Related Art
Power steering systems are commonly used in automobiles. Conventional power steering systems use hydraulic force to assist the rotation of the steering wheel when steering the automobile. The driver is able to steer with a lighter force with help of the power steering system.
Recently, the use of electrically operated power steering systems referred to as EPS (Electric Power Steering) has been widely spreading. Steering in many automobiles have begun to change from hydraulic power steering systems to the EPS. The EPS has the following advantages compared with the hydraulic power steering system:    (1) fuel consumption is improved due to light-weighted component;    (2) safe steering control can be actively performed by electrical control;    (3) EPS can be incorporated in one part of a system for comprehensively controlling each part of the automobile.
Japanese Patent No. 3410512 (issued May 26, 2003) discloses a method of controlling the EPS.
Japanese Patent No. 3410512 discloses a configuration including an IC card reading unit for inputting characteristic information created by a simulation device that creates the characteristic information controlling the characteristics of the automobile outside the target automobile to the target automobile, and a main computer unit for changing the characteristics of the target automobile based on the characteristic information from the reading unit.
Since the characteristics of the target automobile are set outside, the configuration of Japanese Patent No. 3410512 can set the desired characteristics that agree with the sensitivity of the driver while keeping the equipment of the target automobile simple.
Furthermore, Japanese Patent No. 3222506 (issued Oct. 29, 2001) discloses an electrically operated power steering device including a step of reading an output signal from a steering angle sensor, a step of reading a signal from a vehicle speed sensor, a step of calculating a steering angular speed according to the steering angle, a step of storing the vehicle speed and the steering angular speed, a timer processing step of repeating each step over a predetermined number of times for a predetermined time, a step of deleting the upper limit and lower limit ranges of the data repeated over a predetermined number of times, a step of calculating the average vehicle speed and the average steering angular speed from the remaining data, and a step of determining the characteristics of the driver from the average speed and the average steering angular speed.
Furthermore, Japanese Patent Application Laid-Open No. 07-156817 (Jun. 20, 1995) discloses the following electrically operated power steering device. The electrically operated power steering device is configured by a steering torque sensor, a steering rotational speed sensor, a controlling unit, an electrical motor driving unit and an electrical motor. The controlling unit calculates a correction value of the product of a torque attenuation coefficient corresponding to a torque signal and a rotational speed control amount corresponding to the steering rotational speed signal, and generates an electrical motor control signal subtracted or added between the torque control amount corresponding to the torque signal and the correction value in correspondence to going state or returning state of the steering.
Japanese Patent Application Laid-Open No. 08-161004 (Jun. 21, 1996) and Japanese Patent Application Laid-Open No. 08-115102 (May 7, 1996) also disclose background art, although not described in detail herein.